Cardiac pacemakers are cardiac rhythm management devices that provide electrical stimulation in the form of pacing pulses to selected chambers of the heart. (As the term is used herein, a pacemaker is any cardiac rhythm management device that performs cardiac pacing, including implantable cardioverter/defibrillators having a pacing functionality.) Cardiac rhythm management devices are typically implanted subcutaneously on a patient's chest and have leads threaded intravenously into the heart to connect the device to electrodes used for sensing and pacing, the electrodes being disposed in proximity to selected chambers of the heart. Pacemakers typically have a programmable electronic controller that causes the pacing pulses to be output in response to lapsed time intervals and sensed intrinsic cardiac activity.
The most common condition for which pacemakers are used is in the treatment of bradycardia, where the ventricular rate is too slow. If functioning properly, a pacemaker makes up for the heart's inability to pace itself at an appropriate rhythm in order to meet metabolic demand by enforcing a minimum heart rate. Pacing therapy can also be used in the treatment of congestive heart failure (CHF). It has also been shown that some CHF patients suffer from intraventricular and/or interventricular conduction defects such that their cardiac outputs can be increased by improving the synchronization of right and left ventricular contractions with electrical stimulation, referred to herein as ventricular resynchronization therapy.
Modern pacemakers also typically have the capability to communicate data via a radio-frequency link with an external programming device. Such data is transmitted to the pacemaker in order to program its mode of operation as well as define other operating parameters. Data is also transmitted from the pacemaker which can be used to verify the operating parameters as well as relay information regarding the condition of both the pacemaker and the patient. Among the data which may typically be telemetered from the pacemaker are the frequencies at which ventricular sensing and pacing events at particular R-R intervals occur, where an R-R interval is the time between ventricular events that define a cardiac cycle, either a ventricular sense or pace. Such data is typically displayed on the external programmer as a histogram.